The invention relates to a method and to a device for depositing coating material with the manufacture of coated and/or impregnated sheet formations.
There are known a multitude of methods and devices which are used for the manufacture of coated and/or impregnated sheet formations.
With this for example substrates of various materials, such as plastic, sheet metal or fibre-glass may be coated. With fibre sheet formations such as e.g. tissues, fleece and weavings such methods are not only used for coating but also for strengthening and filling the fibre sheet formation.
For coating, one-component as well as two-component systems or mixtures may be provided which in a fluid state may for example be deposited onto the substrate by extrusion or brushing. A particularly known application of such a method lies in the coating of fibre sheet formations for manufacturing so-called xe2x80x9cprepegsxe2x80x9d in printed circuit board manufacture.
With this there exists high demands on the accuracy. The thickness of the coated and/or impregnated sheet formation must remain within very small tolerance regions. Coated sheet formations typically have a thickness of the size order of tenths of millimetersxe2x80x94the tolerances range within the micrometer region.
It has therefore already been suggested (see e.g. non-prepublished PCT application PCT/CH/00513) after the depositing of the coating material to provide an adjustable dimensioning gap which is formed by rollers running against the material web.
It has however been ascertained that with this known method the demanded tolerances may no longer be achieved without further ado. In particular a sufficiently large centricity of roller surface and shaft may not be achieved. A certain out-of-center running of the rollers may therefore not be avoided.
It is therefore the object of the present invention to avoid the disadvantages of that which is known, in particular thus to provide a device and a method for depositing coating material, with which the manufacture of coated and/or impregnated sheet formations is possible with the highest accuracy.
According to the invention this object is achieved with a device and with a method with the features of the characterizing part of the independent patent claims.
The device according to the invention for depositing coating material with the manufacture of coated and/or impregnated sheet formations comprises one or more depositing devices known per se for depositing the coating onto the sheet formations. In the running direction, after the depositing device there is provided a dimensioning gap for dimensioning the thickness of the coated and/or impregnated sheet formation movable through the gap. The width of the dimensioning gap is predeterminable so that the thickness of the coated and/or impregnated sheet formation may be adjusted. The dimensioning gap is limited by at least one metering roller pressable with a contact surface against the sheet formation, and a counter-contact surface. To the metering roller and the counter-contact surface there is in each case allocated a measuring surface. The distance of the measuring surfaces is larger than the dimensioning gap. This permits measuring sensors to be placed between the measuring surfaces, which have no space in the dimensioning gap. In particular the at least one metering roller in the axis direction at at least one end is provided with a cylindrical measuring surface. The cylindrical measuring surface has a smaller diameter than the contact surface of the roller. The device furthermore comprises a measuring arrangement which serves for measuring the distance between the measuring surface and the reference measuring surface which is defined in relation to the counter-contact surface. With the manufacturing procedure of the metering roller and the counter-contact surface the measuring surfaces are formed in an exactly defined position to the contact surfaces.
With the additionally provided measuring surface or surfaces the width of the dimensioning gap may be indirectly very precisely determined. Since the cylindrical measuring surface has a smaller diameter than the contact surface of the roller the distance between the measuring surface and the reference measuring surface with a measuring sensor lying therebetween may be measured without problem. Any occurring out-of-center running between the bearing of the roller and the contact surface of the roller is correctable on account of the measurement of the distance between the measuring surfaces since the measuring surfaces are arranged in an exactly defined relation to the contact surface.
It would however also be conceivable to permit eccentricities between the contact surface and the measuring surface, to determine with a reference measurement and thereafter to compensate by calculation.
According to a particularly preferred embodiment example the counter-contact surface is formed as a second roller. The reference measuring surface is formed as a second cylindrical measuring surface which is arranged at at least one end of the second roller is the axis direction and which has a smaller diameter than the contact surface of the second roller. The second measuring surface is likewise arranged symmetrically and concentrically to the contact surface of the second roller. By way of the fact that the distance between the two cylindrical, concentric measuring surfaces arranged at a known distance to the contact surfaces is measured, indirectly the width of the dimensioning gap may be very accurately determined.
Advantageously the two rollers rotate in the opposite direction to the movement direction of the sheet formation. According to a particularly preferred embodiment example the cylindrical measuring surface or surfaces have a diameter which correspond to more than 50%, advantageously about 70% of the diameter of the contact surface or of the contact surfaces of the roller or rollers. The diameter of the measuring surface is to be selected as large as possible. The closer the measuring surfaces lies to the contact surface the better eccentricities may be avoided since the (smaller) distance between the measuring surface and the contact surface may be more precisely controllable. The measuring surface may however not have the same diameter as the contact surface. In this case the measuring surfaces would lie so close to one another that no sensors may be positioned therebetween. Furthermore there would exist the danger of contamination of the measuring surface by the coating material doctored off with the roller.
According to a further preferred embodiment example the rollers are rotatably mounted such that the bearing of the one roller is fixed and that the bearing of the other roller with respect to the first roller is displaceable perpendicular to the movement direction of the sheet formation. The thickness of the dimensioning gap may be adjusted by displacing the second roller towards the first roller or away from this.
According to a preferred embodiment example the two rollers are pressed together with a predetermined force by pneumatics. The displaceable roller for compensating the out-of-center running is pressable outwards or displaceable inwards, against or with the force of the pneumatics, in particular with a piezoelectric element. The application of a piezoelectric element permits in a particularly simple manner a precise adjusting of the thickness of the dimensioning gap in dependence on the measured distance between the measuring surfaces. With such an arrangement the thickness of the dimensioning gap may also be simply controlled (indirectly via the control of the distance between the measuring surfaces). The device may furthermore be provided with an adjusting arrangement for adjusting the gap width. With this it is additionally conceivable to measure the thickness of the coated sheet formation and to control via the adjusting arrangement. The adjustment of the gap width with the piezoelectric element serves for compensating an out-of-center running, the adjusting arrangement serves for the control of the thickness as a whole.
Advantageously furthermore between the contact surface and the measuring surface there may be arranged an undercut. The undercut avoids a contamination of the measuring surface by coating material doctored from the sheet formation with the contact surface.
The roller or the rollers are furthermore in the known manner provided with a doctor blade with which coating material adhering to the contact surface is removed and advantageously led again to the depositing device.
The measuring arrangement consists advantageously of a contactless sensor, for example of an eddy current sensor. Also other sensors, e.g. optical ones would be conceivable.
The method according to the invention for manufacturing coated and/or impregnated sheet formations may be particularly simply carried out with a device of the described type. The coated and/or impregnated sheet formation is led through an adjustable dimensioning gap between two contact surfaces. According to the invention the distance between measuring surfaces which are defined in relation to the contact surfaces and lie at a greater distance to one another than the contact surfaces are measured. In particular the distance between one measuring surface with a smaller diameter than the cylindrical contact surface and a reference measuring surface defined in relation to the second contact surface is measured. Proceeding with the result of this measurement the width of the dimensioning gap is adjusted, preferably controlled. The invention is thus to the first degree based on providing additional measuring surfaces whose mutual distance may be freely selected without limitation on account of the metering roller design.